PERFORMANCE EVALUATION OF HIGH STRENGTH FLY ASH CONCRETE PAVING MIXES

Abstract

Due to advancement in concrete technology during the last two decades, developed countries now commonly use high strength concrete having ultimate compressive strength of 50 to 70 Mpa for all major construction projects. In India, use of such high strength concrete is few and far between. There is no absolute definition of HSC. It depends upon the present technology, requirement and geographical basis. However, ACI defines HSC as cylinder strength equal to or greater than 41 MPa at 28 days of age using normal weight aggregates. HSC is not made with exotic techniques but by normal methods. The key to making HSC lies in a low w/c ratio. Selection of materials and mix proportioning is more critical in HSC than normal strength concrete. The main objective of this study was to illustrate the design methodology of high strength flyash concrete mixes and to investigate the feasibility of its use in rigid pavements. To study the difference in behaviour of HSFC over control concrete, different mixes (0% flyash, 15 % flyash and 25 % flyash) for target strength of 53 MPa as per ACI 211 and various tests 'were performed to determine the structural properties such as compressive strength, flexural strength, split tensile strength, modulus of elasticity, stress strain behaviour, impact resistance and initial drying shrinkage. The feasibility of use of HSFC in pavement was carried out by designing a rigid pavement, laying it and then carrying out semi full scale field study. The slab was tested under different loading conditions (Central, Edge & Corner) and corresponding deflections and strains were measured. The following conclusions can be drawn from the results of HSFC mixes and HSFC slab. It can be concluded that the replacement of cement by flyash in suitable proportion (depending upon the class and fineness of flyash) is very advantageous. It was found that H.S.C. with flyash not only improves performance of concrete but also overcomes the drawbacks of P.C.C. such as formation of internal micro cracks, poor tensile strength, low toughness and little resistance to impact. The H.S.F.C. mixes were found to posses higher flexural and tensile strength, ability to bear much higher stresses, higher life expectancy, improved resistance to impact, and enhanced durability because of improved micro structure.